Human stem cells can also be used to test new drugs and in medical treatments that now require organ donors. The need for organ donors currently outweighs the available supply.

Embryonic stem cells renew themselves through cell division for long periods of time, unlike specialized cells such as nerve cells or blood cells. Because embryonic stem cells proliferate easily, they can offer a virtually unlimited source of cells needed in medical research.

In 1998, scientists first learned how to isolate human embryonic stem cells. They were developed for infertility purposes through in vitro fertilization.

Embryonic stem cells are derived from eggs less than a week old. The embryonic stem cells are then donated for research purposes with the informed consent of the donors.

Embryonic stem cells are derived from eggs fertilized in the laboratory, not in a woman's body.

Opponents of embryonic stem cell research believe that embryos should not be used in stem cell research because those embryos are unborn children.

Sources: National Institutes of Health, University of Wisconsin-Madison,